The present invention relates to a range finder system utilizing superimposed two images.
A conventional range finder is provided with a first window and a second window which are separated by a predetermined base line length distance. Light entered through the first and second windows is combined by a half mirror and is directed to a common eyepiece optical system. The camera user observes superimposed two images of an object via the eyepiece optical system. Between the first window and the half mirror, there is provided a rotatable mirror which deflects incident light such that the degree of superimposition of the two images changes in the direction of the base line. The distance to the object is determined from the angle of rotation of the rotatable mirror when the two images of the-object coincident.
In particular, in an interlocking type range finder, movement of the photographing lens is interlocked with rotation of the rotatable mirror such that the photographing lens focuses on the object when the two object images coincide.
Conventionally, two types of such a coincidence type range finder are known. In a first type, depending on the positional relationship between the objective lens and the half mirror, two objective lenses are provided respectively on two light paths an the object side of the half mirror. In the second type, a single virtual image type objective lens is provided on the eyepiece lens side of the half mirror.
In first type, especially when the objective lens forms a real image, the outline of each of the superimposed two images is clearly observable, and accordingly a clear field of view can be obtained. However, the first type of range finder system has the drawback of relatively high manufacturing costs, since it includes a large number of components and takes time to assemble.
In the second type, on the other hand, the number of component parts is greatly reduced, compared to the first type, and assembly thereof is easier, thus making it possible to reduce manufacturing costs. However, the second type of finder has a drawback in that, since the half mirror is positioned on the object side of the virtual image objective lens, the area of the half mirror will be relatively large, and if the objective lens is a zoom lens, the range in which the images are superimposed is formed and the unclearness of the image outline within this range will change with zooming of the lens, and there will be a significant drop in resolution especially when the zoom lens is located closer to a tele-photo side.